22 



Trans. Acad. Sci. of St. Louis. 



Fig. 1. 



THE POLYTROPE OF SIRE. 



As already mentioned, the polytrope consists of two essential 

 parts ; ( 1) a large metallic circle ( Cg) representing an earthly 



meridian and (2) a 

 Foucault gyroscope 

 mounted on this cir- 

 cle in such a manner 

 that it may be fixed 

 at any point of it, 

 thus demonstrating 

 the influence of the 

 earth's rotation on 

 the gyroscope at any 

 latitude, 

 j^ The Foucault gy- 

 roscope consists of 

 the torus, or gyros- 

 cope proper ( T) and 

 two circular rings 

 ((7j) and ((?,). The 

 torus rotates freely 

 about the diameter 

 JVN' of the circle ( Cj, while the ring ( CJ itself revolves 

 freely about the diameter PP ' of the circle (Cj, the axes 

 i^iV' and PF' being per- 

 pendicular to one another. 

 The diameter ZZ' of the 

 circle (C^) is perpendicular 

 to PP' and may be fixed in 

 any direction we please rel- 

 atively to the meridian 

 circle ( 6^). 



The origin of the axes 

 XYZ is taken in the center 

 of gravity (0) of the gy- 

 roscope. This coordinate 

 system is fixed with regard 

 to the meridian circle ( C^ ) 



Fig. 2. 



p (^Gyroscope) 



which revolves about its ver- 



